In April 1815, Indonesia's Mount Tambora produced the most powerful eruption in recorded history. Sulphur aerosols injected into the stratosphere dimmed the Sun and cooled the Northern Hemisphere. In 1816, summer frosts and snowfalls wrecked harvests in Europe and North America, triggering famine and riots.
On 27 August 1883, the eruption of the Indonesian volcano Krakatoa was heard as far away as Rodrigues Island, nearly 4,800 km away. Its pressure wave was picked up by barometers worldwide and circled the globe several times. The tsunamis that followed killed more than 36,000 people.
The deepest known point in the ocean, Challenger Deep, lies roughly 10,900 m below the Pacific surface. Drop Everest in and its summit would still sit about 2 km underwater. Down there, the pressure is more than 1,000 times what you feel at sea level, roughly a tonne pressing on every square centimetre.